1. Reversible Reactions and Equilbrium
Prentice-Hall
Chapter 18.2

2. Objectives
Describe how the amounts of reactants and products change in a chemical system at equilibrium.
Identify three stresses that can change the equilibrium position of a chemical system.
Explain what the value of Keq indicates about the position of equilibrium.

3. In the early 1900s, German chemists refined the process of making ammonia from elemental nitrogen and hydrogen. This process allows the manufacture of nitrogen fertilizers.

4. Reversible Reactions
At chemical equilibrium, no net change occurs in the actual amounts of the components of the system.
A reversible reaction is one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously.

5. Equilibrium
If the rate of the shoppers going up the escalator is equal to the rate of the shoppers going down, then the number of shoppers on each floor remains constant, and there is an equilibrium.

6. SO3 decomposes to SO2 and O2
react to give SO3
SO3 decomposes to SO2 and O2
At equilibrium, all three types of molecules are present.

7. When the rates of the forward and reverse reactions are equal, the reaction has reached a state of balance called chemical equilibrium.
The relative concentrations of the reactants and products at equilibrium constitute the equilibrium position of a reaction.

9. Le Châtelier’s Principle
The French chemist Le Châtelier proposed what has come to be called:
Le Châtelier’s principle: If a stress is applied to a system in dynamic equilibrium, the system changes in a way that relieves the stress.

10. Le Châtelier’s Principle
Stresses that upset the equilibrium of a chemical system include:
changes in the concentration of reactants or products
changes in temperature, and
changes in pressure.

11. Concentration
Rapid breathing during and after vigorous exercise helps reestablish the body’s correct CO2:H2CO3 equilibrium, keeping the acid concentration in the blood within a safe range.

12. Temperature
Dinitrogen tetroxide is a colorless gas; nitrogen dioxide is a brown gas. The flask on the left is in a dish of hot water; the flask on the right is in ice.

13. Pressure
Pressure affects a mixture of nitrogen, hydrogen, and ammonia at equilibrium.

18. Equilibrium Constant
The equilibrium constant (Keq) is the ratio of product concentrations to reactant concentrations at equilibrium, with each concentration raised to a power equal to the number of moles of that substance in the balanced chemical equation.

19. Equilibrium Constant
A value of Keq greater than 1 means that products are favored over reactants; a value of Keq less than 1 means that reactants are favored over products.
Keq > 1 products are favored at equilibrium
Keq < 1 reactants are favored at equilibrium

20. Equilibrium Constant

21. Equilibrium Constant

22. Equilibrium Constant

23. Equilibrium Constant

24. Equilibrium Constant

25. Equilibrium Constant

26. Equilibrium Constant

27. Equilibrium Constant

28. Equilibrium Constant

29. Equilibrium Constant

30. 1. In a reaction at equilibrium, reactants and products
decrease in concentration.
form at equal rates.
have equal concentrations.
have stopped reacting.

31. 1. In a reaction at equilibrium, reactants and products
decrease in concentration.
form at equal rates.
have equal concentrations.
have stopped reacting.

32. 2. In the reaction 2NO2(g) ↔ 2NO(g) + O2(g), increasing the pressure on the reaction would cause
the amount of NO to increase.
the amount of NO2 to increase.
nothing to happen.
the amount of O2 to increase.

33. 2. In the reaction 2NO2(g) ↔ 2NO(g) + O2(g), increasing the pressure on the reaction would cause
the amount of NO to increase.
the amount of NO2 to increase.
nothing to happen.
the amount of O2 to increase.

34. 3. Changing which of the following would NOT affect the equilibrium position of a chemical reaction?
concentration of a reactant only
concentration of a product only
temperature only
volume only

35. 3. Changing which of the following would NOT affect the equilibrium position of a chemical reaction?
concentration of a reactant only
concentration of a product only
temperature only
volume only

36. 4. For the following reaction, Keq = 1. A(g) + B(g) ↔ C(g) + D(g)
Therefore, at equilibrium
[C] = [A].
[A][B] = 0.
[AB] = [CD] = 1.
[A][B] = [C][D].

37. 4. For the following reaction, Keq = 1. A(g) + B(g) ↔ C(g) + D(g)
Therefore, at equilibrium
[C] = [A].
[A][B] = 0.
[AB] = [CD] = 1.
[A][B] = [C][D].

38. Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ
Change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
Ni(CO)4(g)
(b)
raise temperature
Keq
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

39. Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ
Change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

40. Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ
Change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

41. ¬ Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

42. ¬ Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

43. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

44. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

45. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

46. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

47. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

48. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

49. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

50. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

51. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)

52. ¬ ® Ni(s) + 4CO(g) ↔ Ni(CO)4(g) ΔHo = - 161 kJ (a) add Ni(s) no change
Direction
of Shift
( ® ; ¬ ; or
no change)
Effect on
Quantity
Effect
(increase, decrease,
or no change)
(a)
add Ni(s)
no change
Ni(CO)4(g)
(b)
raise temperature
Keq
decrease
(c)
add CO(g)
amount of Ni(s)
(d)
remove Ni(CO)4(g)
CO(g)
(e)
decrease in pressure
(f)
lower temperature
(g)
remove CO(g)